1. Field of the Invention
The present invention relates to a semiconductor laser device and a method of method of manufacturing the same, and more particularly to a semiconductor laser device such as a red light laser device, and a method of manufacturing the same.
2. Description of the Related Art
An AlGaInP red light laser device is known as a laser used to record data on recording media such as a digital video disc and a magneto-optic disc. As such a conventional red light laser, a self-aligned structure (SAS) type laser is disclosed in Japanese Patent No. 2502835 as shown in FIG. 1. In this conventional laser device, an n-AlGaInP clad layer 102, an active layer 103 and a p-AlGaInP clad layer 104, a GaInP etching stopper layer 105, a p-AlInP confining layer 106, an n-GaAs blocking layer 107, and a p-AlGaAs upper clad layer 109 are formed on a GaAs substrate 101. The confining layer 106 and the blocking layer 107 have a striped opening section, and the upper clad layer 109 is formed on the etching stopper layer 105 in the striped opening section. That is, the upper clad layer 109 contacts the confining layer 106 and the blocking layer 107 in the striped opening.
The AlInP or AlGaInP layer does not absorb a laser beam and is used for the light confining layer 106 so that it is possible to down an oscillation threshold. However, when the conventional SAS type laser is operated in a high output state, the degradation of the end surface of a resonator occurs due to optical damage such as Catastrophic Optical Damage (COD) which has often occurred in general laser devices. Also, a drive current is injected from the opening section of the confining layer 106 and extends in a lateral direction in the p-AlGaInP clad layer 104. As a result, characteristics such as the oscillation threshold, slope efficiency and kink light output are degraded due to the lateral leakage current.
In conjunction with the above description, a semiconductor laser is disclosed in Japanese patent No. 2,502,835. In the semiconductor laser of this reference, a first conductive type AlGaInP clad layer, an active layer and a second conductive type AlGaInP clad layer are formed on a GaAs substrate of the first conductive type. A striped opening section is formed on the clad layer. The semiconductor laser is composed of an AlInP or AlGaInP confining layer with a refractive index smaller than that of the AlGaInP clad layer of the second conductive type. The semiconductor laser is further composed of a second conductive type upper clad layer formed on the confining layer of the second conductive type containing the opening section and having a wider band gap and lower refractive index than the AlGaInP clad layer.
Therefore, an object of the present invention is provide a semiconductor laser device such as an AlGaInP red light laser device of a SAS-type in which COD on an end surface can be restrained in case of the high output operation, and a method of manufacturing the same.
Another object of the present invention is to provide a semiconductor laser device as a SAS-type laser in which the increase of an oscillation threshold due to lateral leakage current can be restrained, and a method of manufacturing the same.
Still another object of the present invention is to provide a semiconductor laser device as a SAS-type laser in which the decrease of slope efficiency can be restrained, and a method of manufacturing the same.
Yet still another object of the present invention is to provide a semiconductor laser device as a SAS-type laser in which the decrease of kink light output can be restrained, and a method of manufacturing the same.
In an aspect of the present invention, a semiconductor laser device includes an inner lower clad layer formed on a semiconductor layer, an active layer formed on the inner lower clad layer, an inner upper clad layer formed the active layer, a blocking layer formed on the inner upper clad layer to block current, wherein the blocking layer having a concave portion, and an outer upper clad layer formed to cover the blocking layer. Carriers are injected to the active layer through the outer upper clad layer and the concave portion of the blocking layer.
The thickness of the blocking layer in the concave portion is desirably predetermined based on an emission angle and lateral mode of a laser beam emitted from the active layer.
Also, it is desirable that the outer upper clad layer contacts the blocking layer in side walls and a bottom surface of the concave portion. In this case, the thickness of the blocking layer in the concave portion is desirable to be equal to or less than 0.2 xcexcm.
Also, the impurity density of a portion of the inner upper clad layer which corresponds to the concave portion of the blocking layer is desirably higher than that of another portion of the inner upper clad layer and less than an impurity density of the inner upper clad layer. In this case, the impurity density of the inner upper clad layer portion corresponding to the concave portion is desirably more than 3xc3x971016 cmxe2x88x923.
Also, the semiconductor laser device may further include a cap layer formed on the blocking layer. In this case, the cap layer having an opening corresponding to the concave portion of the blocking layer, and the inner upper clad layer is formed on the cap layer and contacts inner walls of the opening and side walls and a bottom surface of the concave portion.
In another aspect of the present invention, a semiconductor laser device is formed by (a) forming an inner lower clad layer on a semiconductor layer; by (b) forming an active layer on the inner lower clad layer; by (c) forming an inner upper clad layer the active layer; by (d) forming a blocking layer on the inner upper clad layer to block current; by (e) forming a concave portion in the blocking layer; and by (f) forming an outer upper clad layer to cover the blocking layer, such that carriers are injected to the active layer through the outer upper clad layer and the concave portion of the blocking layer.
The thickness of the blocking layer in the concave portion is desirably predetermined based on an emission angle and lateral mode of a laser beam emitted from the active layer.
Also, in a method of manufacturing the semiconductor laser device, the outer upper clad layer is desirably formed to contact the blocking layer in side walls and bottom surface of the concave portion. In this case, the thickness of the blocking layer in the concave portion may be equal to or less than 0.2 xcexcm.
Also, the impurity density of a portion of the inner upper clad layer which corresponds to the concave portion of the blocking layer is desirably higher than that of another portion of the inner upper clad layer and less than an impurity density of the inner upper clad layer.
The impurity density of the inner upper clad layer portion corresponding to the concave portion may be more than 3xc3x971016 cmxe2x88x923.
Also, a cap layer is desirably formed on the blocking layer to have an opening corresponding to the concave portion of the blocking layer.
Also, the temperature when the outer upper clad layer may be formed is higher than a temperature when the inner lower clad layer, the active layer, the upper clad layer, and the blocking layer are formed.
Also, an impurity may be injected from the outer upper clad layer into a portion of the inner upper clad layer when the outer upper clad layer is formed.